Interlude

A brief background history and explanation of the Upper Districts Sickness, as given by Urahara Kisuke to Kurosaki Ichigo.

"The upper Rukon districts have always been filled with the worst of spirits that come through Soul Society, but never before have we had so many at once. New districts had to be created just to hold them, and now, with a serious decrease in man-power to police them... we needed some kind of solution before the violence overturned the Rukongai.

"Ah, let me go back a bit. You know, of course, that the Rukongai serves to drain away memory, as a prerequisite to reincarnation. Without Hollows, it would work like a charm, but as it is the Rukongai can't destroy the memories of formerly-Hollow spirits fast enough. Those unfortunate fellows are usually left mentally traumatized by the event - even if they were just eaten by a Hollow and never became a dominating factor, the memories sink in at a very primal level. This leaves a lot of them with violent tendencies, or outright insanity. Historically, these Hollow-influenced spirits are kept in the highest numbered districts, and away from others, but with all the Adjuchas and Hollow deaths during the Arrancar War, we got flooded with more spirits then the traditional districts could handle. Hence, the creation of the Ninetieth through Ninety-Ninth districts.

"Now, though, we can't keep watch over them all, and we can't just wait for the Rukongai to naturally tame them all. So Kyoraku Sotaichou asked me to come up with a solution, which I did.

"Introduce a fake sickness, then counter it with a special medicine to secretly and forcibly erase memories. We say the sickness itself causes memory loss, and our madmen slowly begin to solve our problems themselves, never suspecting the truth.

"I know what you're going to say, probably something about ethics and 'it's our job to protect those spirits,' but that's what we're doing. The lives they lived before were over the moment they were sent to Soul Society, one way or another. Right now, we're simply making the afterlife as safe for as many people as possible."

A quick historical note on the Walls of Seireitei, given by First Division Lieutenant Ise Nanao during a lecture at the Shino Academy.

"Seireitei was once protected by a mineral called Sekkiseki, which made up the original walls, elements of the gates, and certain buildings within Seireitei. The Shinigami Women's Association was responsible for the mineral's eventual banning in use for buildings due to the weakening effect it has on those within, and for most prisoners this is a sentence akin to mental torture. Later, we - I mean the Shinigami Women's Association - were able to bring about the replacing of the walls, after the Rukongai Attacks and the failure of Shinigami to respond due to communication errors with the gate guardians. Free travel from Seireitei to the Rukongai was guaranteed afterwards, making safe-guarding the over-crowded Rukongai far easier for all Shinigami involved."